1. Field of the Invention
The present invention relates generally to electrochemical conductivity sensors which are designed for use in measuring and monitoring conductivities of liquids. More particularly, the present invention relates to an electrochemical sensor which is adapted for use in monitoring using conductimetric techniques.
2. Description of Related Art
U.S. Pat. No. 4,631,116, assigned to the present common assignee, discloses a method for monitoring the minor constituents which are present in plating bath solutions which affect plating deposit properties. The method involves applying a predetermined DC potential to a working electrode positioned within the plating bath solution. The DC potential is determined with respect to a reference electrode. A constant AC signal is superimposed on the DC potential. The DC potential is varied at a predetermined rate over a predetermined range which includes potentials which plate and strip the plating deposits.
The AC current of the applied AC signal is measured between the working electrode and a counter-electrode positioned within the plating bath solution as the DC potential is varied over the predetermined range. The measurement of the AC current in relation to varying DC potential is expressed as an AC current spectrum or fingerprint. By optimizing all AC and DC measurement variables, spectra are obtained which contain fine structure and which enable the monitoring of minor plating bath constituents which affect plating deposit properties.
For monitoring the major constituents of plating bath solutions, techniques other than the voltammetric technique described in U.S. Pat. No. 4,631,116 are needed. Commercially available conductivity measuring devices, which have been used for various laboratory and industrial process measurements, generally are not completely satisfactory for in-tank monitoring of plating bath solutions. For any measurements made in the environment of electrochemical plating baths it is necessary to provide devices having certain, desirable characteristics.
For example, in order to conduct the measurements necessary to monitor the conductivity of a plating bath solution, it is important that the electrodes of the conductivity measuring device be shielded from hydrodynamic and electrical interference from the plating bath. Further, it is important that the electrodes be positioned within the device in a manner which allows continuous and uniform passage of plating bath solution into contact with the electrodes. This requirement is necessary to ensure that the plating bath solution to which the electrodes are exposed accurately reflects overall conditions within the plating bath. In addition, a design with flexible materials of construction and inert to the generally corrosive plating bath environment is essential.
In many large scale production facilities, it would be desirable to have a rugged sensor which can withstand continual rough treatment while still providing extremely accurate measurements. The sensor should also be easily assembled and disassembled to allow cleaning and inspection. Further, the sensor should be constructed so that different electrodes may be put into the sensor to allow measurement of conductivities in many different types of liquids. In addition it would be desirable to be able to use the sensor for measuring the conductivities of solutions of widely varying concentrations.
As is apparent from the above, there presently is a need for sensor devices which are rugged enough to withstand commercial and industrial scale operations while at the same time providing for continual nonturbulent flow of solution into contact with the sensor electrodes in order to provide accurate analysis of a variety of liquids.